Biomass material is increasingly used as a source of thermal energy and to produce bio-plastics and other renewable bio-products. For instance, some residential, institutional and industrial buildings have already been designed or converted to use biomass pellets, instead of fossil fuels, for heating and/or process use. Overall, a number of equipment, including dryers, boilers, and furnaces, continue to be converted to biomass use, instead of fossil fuels. Moreover, recent developments in the forestry field show that wood derivatives, such as nanocrystalline cellulose, may substitute fossil originating chemicals in the production of plastics, textile and other products.
The biomass material used in these applications is typically sourced from waste streams in a number of industries, including the extraction and transformation of wood and agricultural products. In their raw form, biomass by-products usually have a high moisture content and a large particle size, making them ill-suited for direct use in modern biomass applications.
In some cases, raw biomass by-products are used directly in thermal processes, using out-dated and conventional methods, such as moving grate or fluidized bed technologies, which implicates large-sized equipment. This approach results in important energy losses in the process, as well as high levels of flue gas emissions requiring more elaborate emission control systems.
In order to tackle these limitations, conditioning processes of the raw biomass have been developed. The raw biomass is dried to a moisture content of 10% or less, and is grinded to a particulate size ranging from a few microns to a few millimeters, depending on the application.
Typically, the biomass industry relies on a combination of grinders and rotary dryers to perform the above-described conditioning process. This solution is problematic, because the drying system itself relies on a burner which burns some of the dried biomass, in order to provide heating energy for the raw biomass; therefore, an emission control system is a necessary addition to this configuration. Moreover, there are overwhelming capital requirements implicated in the installation of rotary dryers and necessary auxiliary systems, as well as the construction of large-sized building to house the entire system.
In general, all types of dryers (including rotary dryers, flash tube dryers, etc.) rely on a thermal process which i) cannibalizes a portion of the dry biomass production to feed a burner that provides heating energy to raw biomass, ii) requires an emission control system to treat flue gases, and iii) implicates a capital requirement that is uneconomical for small and medium plant capacities.
Furthermore, the existing biomass drying and grinding technologies that are currently used to perform the conditioning process are unsteady, energy inefficient and/or have a limited dewatering capacity. In particular, these technologies commonly exhaust vapour and heated air from the drying chamber; in this manner, thermal energy is actually evacuated and therefore wasted from the process.
Some technologies recycle saturated air in the drying chamber, which effectively limits their ability to dewater raw biomass. As the ‘recycled’ air becomes saturated with moisture, it is unable to absorb further moisture. These technologies operate at low temperature, resulting in water condensation and, therefore, in a sticky biomass build-up in the drying chamber and in the single cyclone.
There is therefore a need in the art for a method and a system for conditioning raw biomass.